Do you have any thoughts about why they specified a minimum of 2.5mm² for T+E (and/or why they thought 1.5mm² was OK for MICC)?Sort of.
Kind Regards, John
Kind Regards, John
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- No I had actually said the reverse, although the regs say that dedicated circuits is one way to ensure no overload, I think it is going OTT except maybe the drier.
- No I think radials are a problem as less diversity.
- It is not having sockets close to end, it is having a socket likely with a prolonged heavy load close to end.
- Yes see below.
One should advise the householder, however in the main anything using high power for an extended time will have a designated location, so this is all part of the kitchen design not really down to the householder.
To avoid a long discussion, perhaps you will say why 2.5mm² is limited to the currents that is is.
How do you work that one out?
I'm not sure what you mean. As I often say, I'm no great fan of 20A radials (except in situations in which it is clear that loads will be very low), but because of the relatively low total capacity of the circuit (no more than two fully-loaded 13A outlets), not anything to do with diversity. However, I'm not sure what problem you would/could see with a 32A radial - the same maximum total load as with a 32A ring final, but no concerns about where things were plugged into the circuit.
Sure - but, as I said, if an electrician were sufficiently concerned, and given that they cannot guarantee what will get plugged into which socket in the future, the only thing they could do to 'be certain' would be to make sure that there are no sockets 'too close to the ends of the circuit'. If there are no sockets 'too close to the end', there is obviously no possibility of a heavy load being plugged in too close to the end
Kind Regards, John
I don't understand the question.
For any type of cable, CSA and installation method, we have (presumably empirically-derived) tabulated values of 'maximum current carrying capacity' which, given that the cables have to be adequately protected by OPDs, presumably take into account the characteristics of OPDs - e.g. that a MCB may allow 1.45 x In to flow for at least an hour - and then seemingly plus a fairly generous further 'safety margin'.
That's as true for 2.5mm² T+E, with any installation method, as is is for any other cable - so, as above, what is the question?
Kind Regards, John
I would think that 1.5 T&E is prohibited because the regulation is still written with BS3036 fuses in mind, but that does not explain why 1.5 MICC is allowed, nor why it is not enough to just stipulate the minimum CCC.
Quite.
If I told you (or the regs) that I had a PVC/PVC T+E cable, with a CCC (as installed) of 20A, that should surely be enough to enable you (or the regs) to tell me whether or not it was 'acceptable' for a ring final circuit, shouldn't it (without my telling you what the CSA was)??
Kind Regards, John
How do you think they decide on what numbers to put in the tables (CCC)? What would be the problem if you put too much current through a given cable?
As I wrote ...
That depends upon what you mean by "too much current". As above, I would expect to be able to put at least 1.45 times its tabulated "CCC" through it for at least an hour without any "problem". If I put a lot more than that through it then (obviously assuming that it was not 'adequately protected') one would eventually reach the point at which the PVC would melt and, if the current got really silly, the point at which the copper would melt.
However, none of that answers the question as to why one (or 'the regs' ) should regard any differently two cables of the same type, both with 'tabulated CCCs" (with the installation method utilised) of 20A, just because their conductor CSAs happened to be different.
Kind REgards, John
That is the first thing that goes wrong in PVC insulated cable as you raise the current. So what about MICC?
That's surely not the point? Why should the material of a PVC insulated+sheathed cable with (given its installation method) a tabulated CCC of 20A be more likely to melt (under whatever circumstances you are considering) if its CSA is 1.5mm² than if it is 2.5mm² (with CCC= 20A in both cases)?
Kind Regards, John